The enzyme L gulono-gamma-lactone dehydrogenase (hereinafter referred to as GLDH) provided by the present invention catalyzes the oxidation of L-gulono-gamma-lactone to L ascorbic acid (vitamin C).
Certain enzymes which catalyze the oxidation of L-gulono-gamma-lactone (I) to L-ascorbic acid (II) ##STR1## are known. Nishikimi et al. isolated L-gulono-gamma-lactone oxidase from rat liver (Arch. Biochem. Biophy., 175, 427-435, 1976), goat liver (Arch. Biochem. Biophy., 175, 427-435, 1976) and chicken kidney (Biochemistry, 21, 5076-5082, 1982). These enzymes consist of one subunit and use molecular oxygen as a direct electron acceptor in the oxidation of I to II. The GLDH of the present invention does not utilize molecular oxygen as a direct electron acceptor and consists of three kinds of subunits. Nishikimi et al. also isolated L-galactono-gamma-lactone oxidase from baker's yeast (Arch. Biochem. Biophy., 191, 479-486, 1978). This enzyme catalyzes the oxidation of both L-galactono-gamma-lactone and L-gulono-gamma-lactone to L-ascorbi acid. On the other hand, Bleeg et al. isolated L-galactono-gamma-lactone oxidase from Saccharomyces cerevisiae (Eur. J. Biochem., 127, 391-396, 1982). This enzyme was reported to be active on L-galactono-gamma-lactone, but not active on L-gulono-gamma-lactone. The GLDH of the present invention does not use L-galactono-gamma-lactone as a substrate.
Shigeoka et al. reported the characteristics of crude L-gulono-gamma-lactone dehydrogenase of Euglena gracilis z (Agric. Biol. Chem., 43, 2187-2188, 1979). The enzyme catalyzed the oxidation of both L-gulono-gamma-lactone and L-galactono-gamma-lactone, and was incapable of using oxygen as an electron acceptor. It is known that algac are difficult to handle due to the problems encountered with the growth of these microorganisms, e.g., fragility, cell division and the extended time periods involved.
There exists no report on the isolation of L-gulono-gamma-lactone dehydrogenase of Euglena gracilis z up to now. In addition, there have been no reports up to now on the conversion of L-gulono-gamma-lactone to L-scorbic acid using bacteria. According to the present invention, however, it has been found that bacteria are capable of producing L-ascorbic acid from L-gulono-gamma-lactone. This is the first possibility of such production of L-ascorbic acid from L-gulono-gamma-lactone using bacteria.